Humberto Soto stepped up in class and weight. It proved to be a good change. The 29-year-old Mexican was workmanlike in downing former WBC champ David Diaz via unanimous decision, 115-111, 117-109 and 117-109, in the final fight before the main event at Cowboys Stadium.

Soto sealed the fight with knockdowns in the first and final round. He landed a big left hook in the final minute of the first that forced Diaz to put a glove on the canvas. Diaz fought hard the rest of the way. HBO ringside judge Harold Lederman actually gave Diaz five rounds the rest of the way. One judge agreed while the other two had it 9-3 for Soto. The title was locked up in the 12th when Soto blasted Diaz with another good left hook. Diaz fell forward off balance to the canvas and quickly bounced back to his feet.

The 33-year-old Diaz (35-3-1, 17 KOs) has now lost two-of-three fights. Soto (51-7-2, 28 KOs) has won seven straight and a belt in his third weight class. He outlanded Diaz 160 to 90 at 25-to-14 percent rate. He also landed 132 power punches.